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Cardiovascular disease is the leading cause of morbidity and mortality in the western world and during the last decades it has also become a rapidly increasing problem in developing countries. An estimated 80 million American adults (one in three) have one or more expressions of cardiovascular disease (CVD), such as hypertension, coronary heart disease, heart failure, or stroke. Mortality data show that CVD was the underlying cause of death in 35% of all deaths in 2005 in the United States, with the majority related to myocardial infarction, stroke, or complications thereof. The vast majority of patients suffering acute cardiovascular events have prior exposure to at least one major risk factor, such as cigarette smoking, abnormal blood lipid levels, hypertension, diabetes, abdominal obesity and low-grade inflammation.
Pathophysiologically, the major events of myocardial infarction and ischemic stroke are caused by a sudden arrest of nutritive blood supply due to a blood clot formation within the lumen of the arterial blood vessel. In most cases, formation of the thrombus is precipitated by rupture of a vulnerable atherosclerotic plaque, which exposes chemical agents that activate platelets and the plasma coagulation system. The activated platelets form a platelet plug that is armed by coagulation-generated fibrin to form a blood clot that expands within the vessel lumen until it obstructs or blocks blood flow, which results in hypoxic tissue damage (so-called infarction). Thus, thrombotic cardiovascular events occur as a result of two distinct processes, i.e. a slowly progressing long-term vascular atherosclerosis of the vessel wall, on the one hand, and a sudden acute clot formation that rapidly causes flow arrest, on the other. Without wishing to be bound by theory, it is thought that the present invention solely relates to the latter process.
Recently, inflammation has been recognized as an important risk factor for thrombotic events. Vascular inflammation is a characteristic feature of the atherosclerotic vessel wall, and inflammatory activity is a strong determinant of the susceptibility of the atherosclerotic plaque to rupture and initiate intravascular clotting. Also, autoimmune conditions with systemic inflammation, such as rheumatoid arthritis, systemic lupus erythematosus and different forms of vasculitides, markedly increase the risk of myocardial infarction and stroke.
Traditional approaches to prevent and treat cardiovascular events are targeted: 1) to slow down the progression of the underlying atherosclerotic process; 2) to prevent clot formation in case of a plaque rupture; or 3) to direct removal of an acute thrombotic flow obstruction. In short, antiatherosclerotic treatment aims at modulating the impact of general risk factors and includes dietary recommendations, weight loss, physical exercise, smoking cessation, cholesterol- and blood pressure treatment etc.
Prevention of clot formation mainly relies on the use of antiplatelet drugs that inhibit platelet activation and/or aggregation, but also in some cases includes thromboembolic prevention with oral anticoagulants such as warfarin. Post hoc treatment of acute atherothrombotic events requires either direct pharmacological lysis of the clot by thrombolytic agents such as recombinant tissue-type plasminogen activator or percutaneous mechanical dilation of the obstructed vessel.
Despite the fact that multiple-target anti-atherosclerotic therapy and clot prevention by antiplatelet agents have lowered the incidence of myocardial infarction and ischemic. stroke, such events still remain a major population health problem. This shows that in patients with cardiovascular risk factors these prophylactic measures are insufficient to completely prevent the occurrence of atherothrombotic events.
Likewise, thrombotic conditions on the venous side of the circulation, as well as embolic complications thereof such as pulmonary embolism, still cause substantial morbidity and mortality. Venous thrombosis has a different clinical presentation and the relative importance of platelet activation versus plasma coagulation are somewhat different, with a preponderance for the latter in venous thrombosis. However, despite these differences, the major underlying mechanisms that cause thrombotic vessel occlusions are similar to those operating on the arterial circulation. Moreover, although unrelated to atherosclerosis as such, the risk of venous thrombosis is related to general cardiovascular risk factors, such as inflammation and metabolic aberrations.
Taken together, existing therapy and general risk factor management offers insufficient protection against thrombotic events, both in the arterial and venous circulations, and cannot reverse the severe consequences of such events. This creates a need for development of novel preventive and therapeutic targets, especially more effective approaches that could prevent hazardous tissue ischemia, and ideally at such an early stage that symptoms have not yet occurred.
Interestingly, it has been found that, in an otherwise healthy individual, there is a natural “last line of defense” system, which can be activated if a clotting process, despite preventive measures, should occur in the vasculature. In brief, initiation of a thrombotic mechanism both on the arterial and venous sides of the circulation leads to activation of the innermost cell layer of the blood vessel (the endothelium), and as a response the cells rapidly release large amounts of the clot-dissolving substance tissue-type plasminogen activator (t-PA). This raises luminal t-PA levels to similar levels as with clinical thrombolytic therapy (i.e. administration of recombinant t-PA), but the potency of this endogenous response is 100-fold greater due to the extremely rapid onset of action.
Accumulating clinical, epidemiologic, and experimental data support the notion that if this thromboprotective function of the blood vessel wall is intact, it offers a powerful defense against formation of flow-arresting thrombi. Unfortunately, however, the capacity for acute t-PA release is impaired in several conditions with increased susceptibility to thrombotic events. These include atherosclerosis, hypertension, abdominal obesity, smoking, sedentary lifestyle, and low-grade inflammation. This impairment is most likely due to a diminished synthesis and thereby reduced availability of the fibrinolytic activator in the endothelial cells.
In addition, we and others have shown that the efficiency of the endogenous fibrinolytic response is reduced in patients with increased risk for an atherothrombotic event, such as in atherosclerosis (Osterlund, B., et al. Acta Anaesthesiol Scand 52, 1375-1384 (2008), Newby, D. E., et al. Circulation 103, 1936-1941 (2001)). Recent data suggest that inflammation may be an underlying pathogenetic mechanism behind the suppressed t-PA production in this state. We have shown that prolonged exposure to the inflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1b) causes a marked suppression of the transcription of t-PA (Ulfhammer, E., et al. Journal of Thrombosis and Haemostasis 4, 1781-1789 (2006), Larsson, P., et al. Thromb Res 123, 342-351 (2008)). Interestingly, it is known that the atherosclerotic plaque is associated with a local, potentially severe, inflammatory activation in the vessel wall and it is conceivable that this inflammatory milieu hampers the fibrinolytic response in the specific areas of the vasculature where it is pivotal to retain a high fibrinolytic capacity, thus increasing the risk of thrombotic events. Similarly, it is also likely that the increased incidence of thrombotic events in patients with systemic inflammatory conditions (e.g. autoimmune diseases and the metabolic syndrome), could also be related to a suppressive effect of circulating pro-inflammatory cytokines on t-PA synthesis and/or increased levels of plasminogen activator inhibitor 1 (PAI-1).
Against this background, an alternative fourth approach to reduce the incidence of clinical thrombotic events should be to restore the capacity of the fibrinolytic ‘last line of defense’ system in patients with an impairment of its function. Extensive efforts have been made to find a feasible means for enhancing basal as well as stimulated endogenous fibrinolysis in subjects with a risk factor-associated reduction of fibrinolytic capacity. However, previous attempts to ameliorate t-PA synthesis with e.g. statins and retinoic acid have been disappointing. Other means of increasing fibrinolysis by blocking naturally occurring inhibitors of t-PA activity such as plasminogen activator inhibitor-1 (PAI-1) and carboxypeptidase U (CPU) have also been unsuccessful mainly due to limited drugability, such as poor pharmacokinetic properties of the drug candidates. The fibrinolytic activity of t-PA is inhibited by plasminogen activator inhibitor 1 (PAI-1) through complex-binding to the t-PA molecule. By virtue of its antifibrinolytic effect, PAI-1 diminishes the ability to dissolve blood clots and thereby increase the risk of clinical thrombotic events (Hrafnklsdottir et al, J Thromb Haemost 2004; 2:1960-8).
PAI-1 circulates in low concentrations in plasma (typically around 5-10 ng/mL in morning samples), but in the population plasma PAI-1 concentration shows a marked right-wardly skewed distribution. Generally, circulating PAI-1 levels increase with age. Elevated PAI-1 levels predispose for thrombotic events. On an individual scale, levels above 100 ng/mL are considered to constitute a significant risk factor for cardiovascular events, even in the absence of other traditional risk factors. Moreover, elevated PAI-1 levels are frequently found in patients with obesity-related metabolic disorders such as Type-2 diabetes mellitus and the metabolic syndrome.
Circulating levels of PAI-1 show a pronounced circadian variation, with peak levels around 06:00 hours and a trough around 16:00 hours as illustrated in FIG. 1 (see also e.g. Scheer and Shea, Blood 2014). As expected, the morning PAI-1 rise coincides with the temporal peak incidence for thrombotic events, such as myocardial infarction.
Patients with obesity and/or the metabolic syndrome have higher circulating PAI-1 levels and augmented circadian peaks as illustrated in FIG. 1. Plasma concentrations typically range between 15-60 ng/mL in morning samples in these patients, but levels are non-normally distributed with a pronounced positive skewness. Plasma PAI-1 levels between 100-500 mg/mL in morning samples are not infrequently observed in obese patients with the metabolic syndrome. Thus, patients with obesity and/or the metabolic syndrome are at particular risk of suffering thrombotic events resulting from the inhibitory effect of PAI-1 on the action of t-PA.
Therefore, it would be interesting to prevent cardiovascular events by lowering PAI-1, and more specifically to abrogate the early morning rise in its plasma concentration. This approach would theoretically be even more efficient in patients with obesity and/or the metabolic syndrome.
We have now surprisingly found that valproic acid (VPA) potently reduces plasma PAI-1 levels, with such reduction, and corresponding reduction in PAI-1 activity, allowing for an increase in the activity of endogenous t-PA. Thus, administration of VPA in low doses in a manner such that plasma levels of VPA, or metabolites thereof, coincide with peak plasma levels of PAI-1 allows for an advantageous effect in the treatment or prevention of pathological conditions associated with excess fibrin deposition and/or thrombus formation.
WO 2012/120262 discusses the use of valproic acid in improving or normalizing endogenous fibrinolysis impaired by local or systemic inflammation. However, it provides no suggestion that VPA may inhibit the action of PAI-1 and, therefore, does not suggest the administration of VPA to counteract (i.e. reduce) peak levels of PAI-1, thus providing a treatment (i.e. an improved treatment) for pathological conditions associated with excess fibrin deposition and/or thrombus formation.
US2007/0232528A1 describes controlled release formulations comprising valproic acid for use in the treatment of disorders such as cancer. These disclosures do not suggest the administration of WA to counteract peak levels of PAI-1, for the treatment for pathological conditions associated with excess fibrin deposition and/or thrombus formation, and so do not suggest formulations designed for this use.